Prolonged drought in the Horn of Africa is the immediate cause of the severe food crisis already affecting around 10 million people in parts of Kenya, Ethiopia, Djibouti and Somalia. Rains have failed over two seasons, with a strong La Niña event having a dramatic impact across the east coast of Africa. Now this year's wet season has officially ended, there is little prospect of rain or relief before September.

How far the current conditions, classified by the UN as "pre-famine" – one step down from "catastrophe" – can be attributed to climate change is not clear. The last intergovernment panel on climate change report suggested that the Horn of Africa would get wetter with climate change, while more recent academic research has concluded that global warming will increase drought in the region. However, according to aid agencies, the weather has become more erratic and extreme in recent years. The same area suffered a drought in 2006 as well as flash floods.

Its strategic position at the opening to the Red Sea and its oil and mineral interests have attracted foreign powers for over 150 years, as Alex de Waal, programme director at the Social Science Research Council, points out.

In 2007, the US launched air strikes against suspected al-Qaida cells in Somalia, and its fear that funds could be diverted to terrorist hands has seen the US cut food aid to the area. Northern Kenya and southern Ethiopia have been home to ethnic Somalis for generations, but the populations are marginalised by central governments. The protracted war in Somalia has driven more than 20,000 more Somalis into Kenya in the past two weeks, says the UNHCR. Thousands have also fled drought and fighting in southern Somalia into the equally water-starved border areas of Ethiopia.

The Kenyan government has periodically tried to close its border, although it is now open with 1,200-1,550 refugees a day crossing, according to some reports. They are being drawn to the refugee camp complex at Dadaab, built in 1991 at the beginning of Somalia's civil war. It has a maximum capacity of 90,000 but is now overwhelmed by in excess of 370,000 people.

The World Food Programme has been feeding 4.3million people in Ethiopia, but had to reduce rations in March as funding ran out – in Kenya, it and the Kenyan government are giving food aid to 2.4 million people.